High resolution bathymetric sonar system and measuring method for measuring the physiognomy of the seabed

ABSTRACT

A high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom having an underwater vehicle, an underwater electronic subsystem mounted on the underwater vehicle and containing a transmitter and a receiver, and two sonar arrays mounted symmetrically on two sides of a lower part of the underwater vehicle and being connected to the underwater electronic subsystem through a cable. Each sonar array has a transmitting linear array and three or more parallel receiving linear arrays. The parallel receiving linear arrays are arranged at equal spaces, and the space d between two adjacent parallel receiving linear arrays is λ&gt;d≧λ/2, in which λ is a wavelength of an acoustic wave, and an operation frequency of the parallel receiving linear arrays ranges from 30 kHz to 1200 kHz.

FIELD OF THE INVENTION

The present invention relates to a high resolution sonar technology,more particularly, to a high resolution bathymetric sidescan sonarsystem and a method for measuring the micro-geomorphy of the sea bottom.

BACKGROUND OF THE INVENTION

The apparatuses and methods for measuring micro-geomorphy of the seabottom at present may be summarized as follows: For example, in a paperentitled “Principal Components Array Processing for Swath Mapping” by P.H. Kreautner and J. S. Bird in Proceedings of the IEEE Oceans' 97Conference, October, 1997, and a paper entitled “Beyond Interferometry,Resolving Multiple Angles-of-Arrival in Swath Bathymetric Imaging” by P.H. Kreautner and J. S. Bird in Proceedings of the IEEE Oceans' 99Conference, September, 1999, a sonar array comprised of six equal-spacedparallel linear arrays is presented. The parallel linear arrays are madeof piezoelectric ceramic arranged at regular space and connected to theterminals of the pre-amplifiers and power amplifiers. A watertight housecontaining all of these parts is placed underwater and connected to anoverwater electronic subsystem through a cable. It operates at afrequency of 300 kHz, and transmits simple pulse signal. A “principalcomponent array processing” method is used in signal processing. Thefollowing experiments are performed:

(A) Measurements with a man-made target are performed in a pool. Theman-made target is a good acoustic target made of orthogonal copperpipes. Said target is correctly detected by the sonar system, but theresults of the measurements in connection to the wall of the pool arerather poor.

(B) Experiments are performed in a small lake. The depth of the lake is2-30 meters. The sonar array is mounted on a common tripod, which ispositioned on the lake bottom in front of a small dock. The electronicapparatus is placed on the shore. The results of the experiments showthat the direct arrival echoes from the lake bottom are detected, butnone of the multipath signals generated from the multipath effect isdeleted automatically within the action range, these multipath signalsare retained in the map.

(C) The normal sidescan map is obtained by rotating the sonar arraypositioned in the same small lake with a stepping motor. Only theintensity of the back scattering signal can be displayed on a normalsidescan map. Though the tendency of the variation of the landform ofthe lake bottom may be deduced from said map, the depth of water can notbe obtained.

(D) The sonar array is moved back and forth on one side of a littleship. When the attitude correction is not adopted and the apparatusesfor positioning and navigating is lacking, a three-dimensional acousticimage, i.e., the three-dimensional tendency of the variation of thelandform of the lake bottom, is obtained. Said apparatus is unable togive the precision of depth measurement and contour map. The depth datain the vicinity of the nadir of the sonar are lacking for theexperiments performed in the pool and lake with all of the prior artapparatuses and technologies.

There are two main defects in a prior art bathymetric sidescan sonartechnology. First, the depth data in the vicinity of the nadir of thesonar can not be measured correctly, even said data may be obtained, theerror of measurement is rather large. Second, the echoes arrivingconcurrently from different directions can not be differentiated, sothat the apparatus can not work normally when the multipath effectexists in the underwater acoustic channel, or the landform is complex.Therefore, the precision of measurement, action range, operationefficiency, and adaptability of the sonar are limited seriously. A“principal component array processing” method is used by P. H. Kreautnerand J. S. Bird to perform signal processing. Said method is capable ofdifferentiating the echoes arriving concurrently from differentdirections basically, but it fails to select automatically the wantedechoes from the lake bottom. Besides, both the precision of measurementand the contour map can not be obtained.

In order to overcome the main defect of supplying a poor precision ofmeasurement in the vicinity of the nadir of a prior art bathymetricsidescan sonar, three methods have been adopted ever. The first methodis decreasing the distance between the survey lines, it always leads toa decrease of the action range of one side, thus makes the ranges of twosuccessive measurements being overlapped each other and the efficiencyis decreased notably. The second method is adding subbottom profiler atthe center. The resolution is low, because the beam width of the conicbeam of said instrument is about 40°. In addition, because of its lowerfrequency, the penetration depth of the conic beam into the sea bottomof the water is rather large, this leads to a lower precision of depthmeasurement. The third measure is adding a minitype multi-beam soundingsystem, thus the complexity of the equipment and the price of theequipment are increased.

Second, the prior art method of signal processing of the bathymetricsidescan sonar is the differential phase estimation method. Because theechoes arriving concurrently from different directions can not bedifferentiated when using said method, the action range and theadaptability of the prior art bathymetric sidescan sonar are limitedseriously. In addition, when working on a complex landform, a pluralityof echoes arriving concurrently from different directions may begenerated, thus the precision of measurement of a prior art bathymetricsidescan sonar will decrease significantly.

SUMMARY OF THE INVENTION

The main object of the invention is to overcome the defects andinadequacies of the prior art. One problem concerns the poor precisionof depth measurement obtained by using a prior art bathymetric sidescansonar system and technology when the vicinity of the nadir of the sonaris measured, and the other problem concerns being incapable of providingcontour map.

The another object of the invention is to solve the problem concerns themethod of signal processing of a prior art bathymetric sidescan sonar,wherein the echoes arriving concurrently from different directions cannot be differentiated, so the action range and the adaptability of aprior art bathymetric sidescan sonar are limited seriously, and theprecision of measurement will decrease significantly when working on acomplex landform.

The further object of the invention is to apply the high resolutionbathymetric sidescan sonar system to an underwater vehicle such asautonomic underwater vehicle (AUV), remotely operated vehicle (ROV), andtowed body, and make said sonar system more practical.

To sum up, the invention is capable of providing a high resolutionbathymetric sidescan sonar system having increased precision ofmeasurement, action range, and operation efficiency for measuring thesubmarine micro-geomorphy.

The objects of the invention are realized as follows: the highresolution bathymetric sidescan sonar system for measuring the submarinemicro-geomorphy provided by the invention comprises an underwaterelectronic subsystem mounted on an underwater vehicles and two sonararrays mounted symmetrically on the two sides of the lower part of theunderwater vehicles. The sonar arrays connected to the underwaterelectronic subsystem through a cable. Its characteristics are that saidsonar array comprises a transmitting linear array for transmittinglinear frequency modulated (chirp) signal and three or more parallelreceiving linear arrays made of piezoelectric ceramic and arranged atequal spaces; wherein the transmitting linear array is connected to thelast stage of a power amplifier in the underwater electronic subsystem,the parallel receiving linear arrays are connected to the preamplifierof a receiver in the underwater electronic subsystem, the space betweenthe adjacent parallel receiving linear arrays is d, λ>d≧λ/2, in which λis the wavelength of the acoustic wave, d=λ/2 is preferred, theoperation frequency of the parallel receiving arrays ranges from 30 kHzto 1200 kHz.

The structure diagram of said high resolution bathymetric sidescan sonarsystem is shown in FIG. 2. A host computer controls the operation of thewhole system, and sends the control signal to the transmitter andreceiver by a controller. The transmitter drives the transmitting lineararrays of the sonar arrays positioned at left and right sides transmitacoustic wave laterally, the acoustic echoes from the sea bottom arereceived successively by the parallel receiving linear arrays of thesonar arrays according to the order of time. The parallel receivinglinear arrays convert the acoustic echoes from the sea bottom intoelectrical signals and feed them to the receiver. The output signal ofthe receiver is converted into digital signal by the acquisition of amultiple channel A/D converter, then said digital signal is sent to ahigh-speed digital signal processor. The bathymetric data is obtainedafter performing various operations in the high-speed digital signalprocessor. The results are sent to the host computer. Through thecontroller the data from an attitude sensor and a temperature sensor arealso sent to the host computer. These results are stored in a hard diskor sent to an overwater computer over an Ethernet link. Therefore, whenthe underwater vehicle moves forward continuously, the acoustic wavesare transmitted and the echoes from the sea bottom are received, thusthe depth data are obtained continuously. A contour map of a certainarea of a sea bottom can be obtained after a period of time (see FIG.1).

Wherein said underwater electronic subsystem comprises: the receivers,the transmitters, the multiple channel A/D converter, the high speeddigital signal processor, the I/O controller, and the host computer. Inwhich the transmitting linear array of the sonar array is connectedelectrically to the last stage of the power amplifier, the parallelreceiving linear arrays are connected electrically to the preamplifierof a receiver, the receivers are connected electrically to a multiplechannel A/D converter, the multiple channel A/D converter is connectedelectrically to a high speed digital signal processor, the high speeddigital signal processor is connected electrically to the host computerthat have a hard disk, and the I/O controller is connected electricallywith the host computer, the transmitter, and the receivers (see FIG. 2).Said underwater electronic subsystem further comprises an attitudesensor and/or a temperature sensor, they are connected electrically tothe host computer via the I/O controller.

In addition, in order to debug the whole underwater electronicsubsystem, an overwater computer connected to the host computer over anEthernet link may be included.

Wherein said receivers (see FIG. 3) are comprised of two receiverboards, the number of the channels and the operation frequency of eachof the receiver board are the same as those of the parallel receivingarray to which said receiver board is connected. Each of the receiverboard is comprised of a preamplifier, a time-varying gain controller, aband pass filter, a quadrature demodulator, two low pass filters, andtwo buffer amplifiers. In which the weak signal received by a transduceris sent into the input terminal of the preamplifier, the output terminalof the preamplifier is connected to the input terminal of thetime-varying gain controller, the output terminal of the time-varyinggain controller is connected to the input terminal of the band passfilter, the output terminal of the band pass filter is connected to theinput terminal of the quadrature demodulator, each of the two outputterminals of the quadrature demodulator is connected to the inputterminal of a low pass filter, each of the two output terminals of thetwo low pass filters is connected to the input terminal of a bufferamplifier, and each of the two outputs of the two buffer amplifiers isfed to the multiple channel A/D converter.

Wherein said transmitters (see FIG. 4) are comprised of two transmitterboards, the operation frequency of each of the transmitter board is thesame as that of the transmitting linear array to which said transmitterboard is connected. The transmitter is comprised of a carrier frequencygenerator, a signal converter, a driving stage, a power stage, and atransformer. In which the gate control signal output from the I/Ocontroller is fed to the input terminal of the signal converter, theoutput of the carrier frequency generator is fed to the input terminalof the signal converter, the output terminal of the signal converter isconnected to the input terminal of the driving stage, the outputterminal of the driving stage is connected to the input terminal of thepower stage, the output terminal of the power stage is connected to theinput terminal of the transformer, and the output terminal of thetransformer is connected to the sonar array.

Wherein said multiple channel A/D converter is used basically toperforming data acquisition on the multiple channel quadrature echosignals processed by the receiver. Said multiple channel A/D converteris comprised of a multiple channel analog switch, an A/D converter, aFIFO memory, a logical controller, a clock generator, and DSP extendedbus interface. In which the output terminal of the multiple channelanalog switch is connected to the input terminal of the A/D converter,the output terminal of the A/D converter is connected to the inputterminal of the FIFO memory, the output terminal of the FIFO memory isconnected to the DSP extended bus interface, the output terminal of theclock generator is connected with the logical controller, the output ofthe logical controller is sent respectively to the control signal inputterminals of the multiple channel analog switch, the A/D converter, andthe FIFO memory, the logical controller is also connected with the DSPextended bus interface. The diagram of the multiple channel A/Dconverter is shown in FIG. 5.

Said high speed digital signal processor (see FIG. 6) is comprised of adigital signal processing chip, a dual port RAM, a static RAM (SRAM), alogical controller, a host computer bus interface, and a DSP extendedbus interface. In which said high speed digital signal processor chip isconnected to one input terminal of the dual RAM, the other inputterminal of the dual port RAM is connected with the host computer businterface, the high speed digital signal processor chip is furtherconnected with the static RAM and the DSP extended bus interface, thelogical controller is connected with the high speed digital signalprocessor chip, the static RAM, the dual port RAM, and the host computerbus interface.

Said I/O controller (see FIG. 7) is comprised of the OC gate digitaloutput port, an 8-bit digital input port, a timer, a logical controller,and a host computer bus interface. In which said logical controller isconnected with the host computer bus interface, the timer, the OC gatedigital output port, the 8-bit digital input port, and the D/Aconverter.

The method of the invention for measuring the submarine micro-geomorphycomprises the follow steps:

-   -   (1) Selecting a suitable underwater vehicle according to the        customer's demands, said underwater vehicle may be, for example,        an AUV, a tethered ROV, a towed system, or a boat;    -   (2) Drafting a preliminary overall specifications according to        the customer's demands, combining the theoretical formula of the        standard deviation of phase of the space-time correlation        function of the sonar system with the sonar equation to perform        the design, selecting the main specifications, such as the        operation frequency, the action range, and the pulse width of        the sonar, and the length of the sonar array;    -   (3) Based on the theoretical expression of the phase additional        factor in the space-time correlation function of the sonar        array, selecting the beam width of the element unit of the        linear array of the sonar array and the space between the linear        arrays, thus a good precision of measurement in measuring in the        vicinity of the nadir of the sonar system may be obtained;    -   (4) Selecting the main parameters and repeating the calculations        in steps (2), (3) until the main parameters of the sonar are        fulfilled basically;    -   (5) Making a decision on the number of the equal-spaced parallel        linear arrays to be used, in which the number equals or greater        than three, then performing the analogous calculation with the        SBAD-MSADOAE (Sea Bottom Automatic Detection—Multiple Subarray        Directions Of Arrival Estimation) method of the invention,        determining preliminarily the resolution of the sonar and the        ability for overcoming the multipath effect;    -   (6) Determining the respective main parameters of the sonar, if        the demands are not met, then the steps (2), (3), (4) and (5)        are repeated, until the respective main parameters of the sonar        are determined, then manufacturing two prototypes of sonar        array;    -   (7) Testing the two prototypes of sonar array manufactured in        step (6) in a pool;    -   first, measuring the echoes from the pool bottom, comparing the        measured depth values of the pool with its true depth values,        including the depth values of the pool in the vicinity of the        nadir of the sonar, the measured values should coincide well        with the corresponding true values; second, measuring the        outline of the pool including its wall corners, the measured        values should coincide basically with the corresponding true        values, then the out door tests may be performed;    -   (8) Performing the tests on a lake or sea: testing the sonar        array mounted on an underwater vehicle; performing the data        processing after tests; first, comparing the depth values        measured by the sonar in the vicinity of the nadir of the sonar        with the depth values measured by a high precision bathymeter,        they should be coincidental well; second, operating the        underwater vehicle in a case in which rather serious multipath        effect exists, determining the ability of overcoming the        multipath effect by the measured data, the correct depth values        of the bottom of the water may be given on the finally obtained        maps, without any multipath signal interference;    -   (9) Merging the data measured by sonar with the data from the        attitude sensor on the vehicle and the positioning data to give        a contour map;    -   (10) Giving a grey scale map of the acoustic back scattering        signal;    -   (11) Making the maps, which the customer needs according to the        customer's demands.

The operation procedure of the system of the invention is stated asfollows:

First, the host computer feeds a gate control signal to two transmittersvia an I/O controller, then the transmitters generate high power linearfrequency modulated (chirp) electrical pulses to drive the transmittinglinear arrays mounted on two sides, the transmitting linear arraysconvert the chirp electrical pulses into acoustic pulse signal andtransmit it to the sea bottom; after transmitting, the host computercommands a high speed digital signal processor to start a multiplechannel A/D converter, mean while the host computer feeds a time-varyinggain control (TGC) signal to receivers via the I/O controller, thereceivers start to receive the signals received by the parallel lineararrays mounted on two sides, after amplifying by the receivers, andpassing through a filter, a quadrature demodulator, the signals arechanged into digital signals, then the digital signals are inputted to ahigh speed digital signal processor, the high speed digital signalprocessor processes the digital signals, the results are inputted to thehost computer and stored on a hard disk; when an attitude sensor and atemperature sensor are set in the apparatus, the data from the attitudesensor and the temperature sensor in this time period are also inputtedto the host computer through the I/O controller and stored on the harddisk; up to now a normal operation period of a high resolutionbathymetric sidescan sonar system is finished, the next normal operationperiod of the system shall follow closely, only shutting off theelectricity supply can stop the operation of the system. The flowdiagram of the program run in the host computer is shown in FIG. 11.

The advantages of the invention are:

(1) The sea bottom is regarded as a thin layer generating backscatterechoes when using the high resolution bathymetric sidescan sonar systemand method of the invention to measure the micro-geomorphy of the seabottom. The measured result of said bathymetric sidescan sonar system isshown in FIG. 14. In said figure, the real line represents thetheoretical values; the dotted line represents the measured values. Itcan be seen from this figure that the measured values are in coincidencewith the corresponding theoretical values. However, in the prior art,the sea bottom is assumed as a zero thickness surface which generatesthe back scatter echoes, d=0.7λ is selected when the sidelobe of thesonar array is considered. In the prior art, the reason of causing theerror in measuring the nadir of the sonar is not concerned, and theprecision of depth measurement is not given. In the invention, the seabottom is considered as a thin layer generating back scatter signal, anadditional term called phase additional factor ξ occurs in the derivedexpression of the phase of the space-time correlation function of thesonar array of the bathymetric sidescan sonar as compared with thecorresponding expression of the ordinary theory. The ξ term lowers theprecision of depth measurement when the measured place is in the nadirof the sonar system. As shown in FIG. 8, the space d used in theinvention is: λ>d≧λ/2, this reasonable design parameter is given afteranalyzing the phase additional factor. It can be seen from FIG. 8 thatwhen the space d between the parallel arrays of the sonar array equalsor less than wavelength λ, ξ can affect the precision of depthmeasurement only in a narrow angular width. When d=λ/2, the effect of tis minimum. The theoretical values and the experimental values of thestandard deviation of the phase in the sonar space-time correlationfunction are coincidental well, thus the reason of causing the error inmeasuring the depth of the nadir of the sonar system is found in theinvention. Because of this reason, the precision of depth measurement inmeasuring the depth of the nadir of the sonar system is improvedgreatly. The real precision of depth measurement is superior to 1%.

(2) When measuring with the bathymetric sidescan sonar system of theinvention, a signal processing method named SBAD-MSADOAE methodresearched and invented by us is adopted. The method is capable ofdifferentiating the echoes arriving concurrently from differentdirections, detecting and tracking correctly the directly arrivingechoes from the sea bottom, and deleting the interferential multipathechoes. In connection to the concrete operation situation, for example,deep sea or shallow water, a suitable number of the subarrays may beselected, thus the detection performance can be improved significantly.Adopting reasonable method of signal processing results in increasingthe distinguishability on the coherent signals. In FIGS. 16 and 17obtained by said method, the multipath signal caused by the multipatheffect can not be found.

(3) The high resolution bathymetric side scan sonar system of theinvention may be mounted on an AUV. The practical measurements areperformed when the arrays mounted on the both sides operateconcurrently. The precision of depth measurement and the contour map aregiven in FIGS. 18 and 19 after correcting the errors.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the structure of the invention.

FIG. 2 is a block diagram of the structure of the high resolutionbathymetric sidescan sonar system of the invention.

FIG. 3 is a diagram of the circuital structure of one channel of thereceiver of the high resolution bathymetric sidescan sonar system of theinvention.

FIG. 4 is a diagram of the circuital structure of the transmitter of thehigh resolution bathymetric sidescan sonar system of the invention.

FIG. 5 is a diagram of the circuital structure of the multiple channelA/D converter of the high resolution bathymetric sidescan sonar systemof the invention.

FIG. 6 is a diagram of the circuital structure of the high speed digitalsignal processor of the high resolution bathymetric sidescan sonarsystem of the invention.

FIG. 7 is a diagram of the circuital structure of the I/O controller ofthe high resolution bathymetric sidescan sonar system of the invention.

FIG. 8 is a figure showing the relationship between the phase additionalfactor ξ and the acoustic wave grazing angle θ. Curve I is the resultwhen d=0.5λ, Curve II is the result when d=λ, Curve III is the resultwhen d=10λ. It can be seen from the figure that the effect of ξ israther small when d≧λ, and the effect of ξ is minimum when d=0.5λ.

FIG. 9 is a diagram of the geometrical situation of the operation of thehigh resolution bathymetric sidescan sonar system of the invention. Itcan be seen from the figure that a plurality of echoes may be generatedby the sea bottom and the surface of the water; this is the so-calledmultipath effect of the underwater acoustic channels. In addition, thecomplex sea bottom is also capable of generating a plurality of echoesarriving concurrently from different directions.

FIG. 10 is a diagram of the structure of the sonar array of the highresolution bathymetric sidescan sonar system of the invention.

FIG. 11 is a flow diagram illustrating the program stored in the memoryof the computer for controlling the high resolution bathymetric sidescansonar system of the invention.

FIG. 12 is a figure for comparing the experimental data of a poolobtained by using respectively the method of the invention and the priorart method. The detected target is the pool bottom. Because themultipath effect exists, the method of the invention is superior to theprior art method. The method of the invention is capable of giving thedepth data in the vicinity of the nadir of the sonar:

FIG. 12(a) (upper) is a figure showing the relationship between thegrazing angle and the time. In the figure, --- (real line) representsthe result of the theoretical value, - - - (dash line) represents theresult obtained by the method of the invention, -•- (dash dot line)represents the result obtained by the prior art method. It can be seenfrom the figure that the SBAD-MSADOAE method of the invention issignificantly superior to the prior art method.

FIG. 12(b) (lower) is a figure showing the relationship between thedepth and the distance. In the figure, the mark □ (square) shows theposition of the transducer, the mark ◯ (circle) represents the resultsobtained by the method of the invention, and the mark * (star)represents the results obtained by the prior art method. The figureshows that the method of the invention is significantly superior to theprior art method.

FIG. 13 shows the results detected for the wall of the pool (the cornersof the pool are included) by the method of the invention. In the figure,the mark □ (square) shows the position of the transducer, and the mark ◯(circle) represents the result obtained by the method of the invention.The results are in coincidence basically with the outline of the pool.Because of serious multipath effect, the prior art method fails to giveany useful data.

FIG. 14 is a figure showing the relationship between the standarddeviations of the space-time correlation function of the sonar array ofthe invention and the horizontal distances. In the figure, --- (realline) represents the results of the theoretical values, the mark *(star) represents the results obtained from the experimental value. Itcan be seen from the figure that the theoretical values are incoincidence well with the experimental values of the embodiment of theinvention.

FIG. 15 is a figure showing the comparison of the depth data measured inthe vicinity of the nadir of the sonar between the system of theinvention and a high precision depth sounder; both of them are mountedon an AUV. It can be seen from the figure that the results obtained fromthem are coincidental well. The main specifications of the highprecision depth sounder are: operation frequency: 300 kHz, beam width4°, pulse width 0.1 ms, transmitting 10 times per second.

FIG. 16 are figures showing the comparison of the data obtainedrespectively by the SBAD-MSADOAE method of signal processing of theinvention and the prior art method for an acoustic emission on thestarboard. The data obtained by the method of the invention are stillreasonable until the number of the beam reaches 200-250 and thehorizontal distance reaches 200-250 m; while the data obtained by theprior art method can be regarded as reasonable only when the number ofbeams does not exceed 80 and the horizontal distance is less than 80 m.In which FIG. 16 a is a figure shows the relationship between the numberof the beams and the grazing angle, FIG. 16 b is a FIG. 5 shows therelationship between the horizontal distance and the depth.

FIG. 17 are figures showing the comparison of the data obtainedrespectively by the SBAD-MSADOAE method of signal processing of theinvention and the prior art method for an acoustic emission on the port.The conclusions are the same as those deduced for FIG. 16. In which FIG.17 a is a figure shows the relationship between the number of the beamsand the grazing angle, FIG. 17 b is a figure shows the relationshipbetween the horizontal distance and the depth.

In FIGS. 15-17, --- (real line) represents the results obtained by themethod of the invention; - - - (dash line) represents the resultsobtained by the prior art method.

FIG. 18 is a three-dimensional depth profile map, which is obtained withthe data obtained from 300 acoustic emissions transmitted by the highresolution bathymetric sidescan sonar system.

FIG. 19 is a contour map, which is obtained with the data obtained from300 acoustic emissions transmitted by the high resolution bathymetricsidescan sonar system. Wherein,

1-underwater electronic subsystem 2-underwater vehicle 3-left sonararray 4-right sonar array 5-receiving linear array A 6-receiving lineararray B 7-receiving linear array C 8-receiving linear array D9-transmitting array 10-receiving array 11-received electrical signal12-transmitted electrical signal 13-surface of water 14-pool bottom15-pool wall

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1:

A high resolution bathymetric sidescan sonar system for measuring themicro-geomorphy of the sea bottom is manufactured according to FIGS. 1and 2. The targets to be detected are the pool bottom, the pool wall andthe surface of water. Said sonar system comprises: any one of the sonararrays 3, 4 dipped into a pool by a dipping means, the sonar array isconnected to the underwater electronic subsystem with a cable, theunderwater electronic subsystem is placed on a working table on thesurface of the water. Each of the sonar array is comprised of onetransmitting linear array for transmitting linear frequency modulated(chirp) signals and four parallel linear arrays A, B, C, D arranged atequal space and made of piezoelectric ceramic. The space between twoadjacent parallel receiving arrays d=λ, λ=2 cm. The length of the lineararray is 70 cm. The operation frequency ranges from 30 kHz up to 1200kHz. The transmitting array 9 is connected to the last stage of a poweramplifier of the transmitter of the underwater electronic subsystem 1,the parallel receiving linear arrays A-D are connected to a preamplifierof a receiver of the underwater electronic subsystem 1, the receiver iselectrically connected to a multiple channel A/D converter, the multiplechannel A/D converter is electrically connected to a high speed digitalsignal processor, the high speed digital signal processor iselectrically connected to a host computer that have a hard disk, an I/Ocontroller is electrically connected with the host computer, thetransmitter, and the receiver. The sonar system is shown in FIG. 10. Theoperation frequencies of the two sides of the sonar are 70 kHz and 80kHz, respectively. The connection relationship between the respectiveparts of the underwater electronic subsystem of the high resolutionbathymetric sidescan sonar and the sonar arrays is shown in FIG. 2. Thehost computer feeds a gate control signal to the two transmitters via anI/O controller, then the transmitters generate high power linearfrequency modulated (chirp) electrical pulses to drive the transmittinglinear arrays on the two sides, the transmitting linear arrays convertthe chirp electrical pulses into acoustic pulse signal and transmit ittoward the sea bottom; after transmitting, the host computer commands ahigh speed digital signal processor to start a multiple channel A/Dconverter, mean while the host computer feeds a time-varying gaincontrol (TGC) signal to receivers via the I/O controller, the receiversstart to receive the signal received by the parallel linear arrays onthe two sides, after amplifying by the receivers, and passing through afilter, a quadrature demodulator, the signals is changed into digitalsignals, then the digital signals are inputted to a high speed digitalsignal processor, the high speed digital signal processor processes thedigital signals, the results are inputted to the host computer and storeon a hard disk; when an attitude sensor and a temperature sensor are setin the apparatus, the data from the attitude sensor and the temperaturesensor in this time period are also inputted to the host computerthrough the I/O controller and store on the hard disk. The constitutingparts are illuminated respectively as follows: FIG. 3 is a circuitdiagram of one channel of the receiver. Each of the channels comprises:a preamplifier, a time-varying gain controller, a band pass filter, aquadrature demodulator, two low pass filters, and two buffer amplifiers.They are connected in sequence according to the run of the signal shownin FIG. 3. The part corresponding to each of the blocks in FIG. 3 is acommercially available special-purpose chip. FIG. 4 is a circuit diagramof the transmitter comprising a signal converter, a driving stage, apower stage, and a transformer. They are connected in sequence accordingto the run of the signal shown in FIG. 4. All of them, except thetransformer, are commercially available. The transformer is a normalpulse transformer. FIG. 5 is a block diagram of the multiple channel A/Dconverter comprising: an analog input unit, a multiple channel analogswitch, an A/D converter, a FIFO memory, a logical controller, a clockgenerator, a host computer bus interface, and a DSP extended businterface. They are connected in sequence according to the run of thesignal shown in FIG. 5. FIG. 6 is a block diagram of the high speedsignal processor comprising: a chip for digital signal processing, adual port RAM, a static RAM (SRAM), a logical controller, and a DSPextended bus interface. They are connected in sequence according to therun of signal shown in FIG. 6. FIG. 7 is a block diagram of the circuitof the I/O controller comprising: an OC gate digital output unit, an8-bit digital input unit, a timer, a D/A converter, a logicalcontroller, and a host computer bus interface. They are connected insequence according to the run of the signal shown in FIG. 7. Each of thedigital chips in FIGS. 5, 6, 7 is a commercially availablegeneral-purpose chip. The measured results for the pool bottom using theSBAD-MSADOAE method of the invention and the prior art method are givenin FIG. 12. In FIG. 12 a, the dash line represents the results obtainedby the SBAD-MSADOAE method of the invention, the dash and dot linerepresents the results obtained by the prior art method (differentialphase method), and the real line represents the theoretical values. Itcan be seen from the figure that the results obtained by the method ofthe invention are close to the theoretical values, and significantlysuperior to the prior art method. The position of the sonar array isnotated in FIG. 12 b. The mark represents the results of the method ofthe invention, the mark * represents the results of the prior artmethod. The results obtained by the method of the invention aresignificantly close to the bottom of the pool marked with real line. Thetargets to be detected in FIG. 13 are the pool bottom, the pool wall andthe surface of the water, and the pool corners are included as well. Thedata in FIG. 13 is obtained by the method of the invention, which are incoincidence with the pool bottom basically. The useful data can not beobtained by the prior art method because of the serious multipatheffect. It can be seen from the figure that not only the depth of nadirof the sonar, but also the positions of the wall of the pool and thesurface of the water can be detected. These can not be detected by theprior art method.

It can be seen from FIG. 9 the geometrical situation of the operation ofthe high resolution bathymetric sidescan sonar system. The echoes fromdifferent directions may arrive the sonar array concurrently because ofthe multiple reflection of the surface of the water and the sea bottom,and the echoes generated due to the complex bottom landform. In order todifferentiate these echoes and find out the required echoes from the seabottom, two sonar arrays are developed by the inventor. They are mountedon both two sides of the underwater vehicle. Each of the sonar arrayscomprises a transmitting array and four parallel receiving lineararrays. The operation frequency ranges from 30 kHz to 1200 KHz. Thetransmitting array transmits linear frequency modulated (chirp) signal.The arrangement of the sonar array is shown in FIG. 10. 16 space-timecorrelation functions can be obtained with four parallel receivinglinear arrays, and a 4×4 matrix is constructed with these 16 space-timecorrelation functions. This matrix contains a great amount ofinformation concerning the amplitude, phase, frequency, and grazingangle of the echoes. One of the principal objects of the invention is tosolve this matrix and separate the echoes arriving concurrently fromdifferent directions.

Embodiment 2:

A high resolution bathymetric sidescan sonar system taking the lakebottom as the object to be measured is manufactured according to FIGS.1-7, 10, and 11. Said system is set on the CR-02 AUV. The underwaterelectronic subsystem 1 and sonar arrays 3, 4 are mounted on said AUV 2,wherein said sonar arrays 3, 4 are mounted symmetrically on the bothsides of the lower portion of the AUV 2. The construction of theunderwater electronic subsystem is the same as that in the embodiment 1.The AUV 2 moves over the lake bottom at a height of 40-60 m and measuresthe micro-geomorphy of the lake bottom with the method of the invention.Said system still comprises two sonar arrays, each of the sonar arrayscomprises a transmitting linear array and four parallel receiving lineararrays made of piezoelectric ceramic. The space of the linear arraysd=λ, λ=2 cm. The length of the linear array is 70 cm. The structure ofthe electronic subsystem is the same as that in embodiment 1. The resultof depth measurement in the vicinity of the nadir of the AUV 2 by themethod of the invention is given in FIG. 15. In the figure, the realline represents the measured results by the high resolution bathymetricsidescan sonar system of the embodiment 2, the dash line represents themeasured results by the high resolution digital depth sounder. Thetechnical specifications of the high resolution digital depth sounderare: operation frequency: 300 kHz, beam width: 4°, pulse width: 0.1 ms,transmitting rate: 10 times per second. It can be seen from the figurethat the results obtained by both two methods coincide well. Thissituation indicates that the bathymetric precision may be achieved bythe method and system of the invention. Such result can not be given bythe prior art method. The results of depth measurement of the inventionare shown in FIGS. 16, 17. FIG. 16 shows the measured results by thehigh resolution bathymetric sidescan sonar mounted on the AUV. The realline represents of the method of the invention, and the dash linerepresents the results of the prior art method. FIG. 16 a is a figureshowing the relationship between the number of the beams and the grazingangle. It can be seen from the figure that the data obtained by themethod of the invention are still reasonable until the number of thebeam reaches 200, but the data obtained by the prior art method can beregarded as reasonable only when the number of beams does not exceed 80.FIG. 16 b is a figure showing the relationship between the horizontaldistance and the depth. It can be seen from the figure that the dataobtained by the method of the invention are still reasonable until thehorizontal distance reaches 200 m; but the data obtained by the priorart method can be regarded as reasonable only when the horizontaldistance is less than 80 m. FIG. 17 is the measured result of the otherside, the reference signs and the conclusions are the same as those inconnection to FIG. 16. It can be seen that the multipath signal iseliminated by the method and system of the invention, but the prior artmethod does not possess this capability. The precision of depthmeasurement, action distance and adaptability of the bathymetric sidescan sonar system are increased significantly by the method of theinvention. Besides, as shown in FIGS. 18, 19, three dimensional depthprofile map and contour map (including the depth data of the nadir ofthe sonar) can be obtained by merging the data measured by the methodand system of the invention and the attitude data and the positioningdata of the underwater vehicle. These results can not be obtained by theprior art method and system.

The sonar system of the invention of this embodiment as well as anattitude sensor and a navigation positioning sensor are mounted on theAUV and systematic tests are performed in a deep-water lake (its maximumdepth is 150 m) for a long time. The following conclusions may beobtained from the experimental data:

a. As shown in FIG. 14, the theoretical values and the experimentalvalues of the standard deviation of the phase of the space-timecorrelation function of the sonar array are coincidental well. This factproves the correctness of our theory that is the theoretical basis ofthe high resolution bathymetric sidescan sonar system.

b. As shown in FIG. 15, as to the place in the vicinity of the nadir ofthe AUV, the depth data obtained from the AUV and the data obtained froma high resolution depth sounder mounted on the bottom of the AUV arecoincidental well, the precision of depth measurement is superior to 1%.This fact proves the correctness of our theory. This makes thepracticableness of the high resolution bathymetric side scan sonar. Thetechnical specifications of the high precision depth sounder are:operation frequency: 300 kHz, beam width: 4°, pulse width: 0.1 ms,emission rate: 10 times/sec.

c. The multipath signal of the underwater acoustic channel can beseparated completely by the SBAD-MSADOAE method of the invention. Inlight of this method, we can detect and track the bottom of water,delete the multipath signal, and obtain FIGS. 16, 17 without remainmultipath signal.

d. We are capable of obtaining the corrected depth profile map (threedimensional depth map) for an extensive region, see FIG. 18.

e. We are capable of obtaining the corrected contour map for anextensive region, see FIG. 19.

For the purpose of understanding, the invention has been described withreference to Drawings and specific embodiments, but this description isnot meant to be limited in these embodiments. Various modifications tothe disclosed embodiments as well as alternative embodiments of theinvention will become apparent to those skilled in the art uponreference to the description of the invention.

1. A high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom comprising: an underwater vehicle, an underwater electronic subsystem mounted on the underwater vehicle and comprising a transmitter and a receiver, and two sonar arrays mounted symmetrically on two sides of a lower part of the underwater vehicle, and being connected to the underwater electronic subsystem through a cable, wherein the transmitter comprises a power amplifier having a last stage and the receiver comprises a preamplifier, wherein each sonar array comprises a transmitting linear array for converting a linear frequency modulated signal at an output of said transmitter into an acoustic pulse signal and transmitting said acoustic pulse signal to the sea bottom, said transmitting linear array being connected to the last stage of the power amplifier, and three or more parallel receiving linear arrays made of piezoelectric ceramic connected to the preamplifier of the receiver; and wherein the parallel receiving linear arrays are arranged at equal spaces, and the space d between two adjacent parallel receiving linear arrays is [d,] λ>d≧λ/2, in which λ is a wavelength of an acoustic wave, and an operation frequency of the parallel receiving linear arrays ranges from 30 kHz to 1200 kHz.
 2. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 1, wherein the space between the two adjacent parallel receiving linear arrays d is λ/2.
 3. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 1, wherein said underwater electronic subsystem further comprises: multiple receivers, multiple transmitters, a multiple-channel A/D converter, a high speed digital signal processor, an I/O controller, and a host computer, wherein the receivers are connected electrically to the multiple-channel A/D converter, the multiple-channel A/D converter is connected electrically to the high speed digital signal processor, the high speed digital signal processor is connected electrically to the host computer having a hard disk, and the I/O controller is connected electrically with the host computer, the transmitters, and the receivers.
 4. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 3, wherein said underwater electronic subsystem further comprises an attitude sensor, a temperature sensor, or both, and the attitude sensor and the temperature sensor are connected electrically to the host computer via the I/O controller, respectively.
 5. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 3, wherein said receivers comprise two receiver boards a number of channels, and and a the number of the parallel receiving arrays to which said receiver boards are connected is the same, and each of the receiver boards operates at the same frequency; and wherein each of the receiver boards comprises a preamplifier, a time-varying gain controller, a band pass filter, a quadrature demodulator, two low pass filter, and two buffer amplifiers, wherein a weak signal received by a transducer is sent into an input terminal of the preamplifier, an output terminal of the preamplifier is connected to an input terminal of the time-varying gain controller, an output terminal of the time-varying gain controller is corrected to an input terminal of the band pass filter, an output terminal of the band pass filter is connected to an input terminal of the quadrature demodulator, each of two output terminals of the quadrature demodulator is connected to an input terminal of a respective low pass filter, each of the output terminals of the two low pass filters is connected to an input terminal of each of two buffer amplifiers, and the output of each of the two buffer amplifiers is fed to the multiple-channel A/D converter.
 6. (canceled)
 7. The high resolution bathymetric sidescan sonar system according to claim 3, wherein said transmitters comprise two transmitter boards, their operation frequency is the same as that of the transmitting linear array to which said transmitters are connected; each transmitter comprises a carrier frequency generator, a signal converter, a driving stage, a power stage, and a transformer; in which a gate control signal outputted from the I/O controller is fed to an input terminal of the signal converter, an output of the carrier frequency generator is fed to an input terminal of the signal converter, an output terminal of the signal converter is connected to an input terminal of the driving stage, an output terminal of the driving stage is connected to an input terminal of the power stage, an output terminal of the power stage is connected to an input terminal of the transformer, and an output terminal of the transformer is connected to the sonar array.
 8. (canceled)
 9. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 3, wherein said multiple-channel A/D converter comprises a multiple-channel analog switch, an A/D converter, a FIFO memory, a logical controller, a clock generator, and DSP extended bus interface, wherein an output terminal of the multiple-channel analog switch is connected to an input terminal of the A/D converter, an output terminal of the A/D converter is connected to an input terminal of the FIFO memory, an output terminal of the FIFO memory is connected to the DSP extended bus interface, an output terminal of the clock generator is connected with the logical controller, an output of the logical controller is sent respectively to control signal input terminals of the multiple-channel analog switch, the A/D converter, and the FIFO memory, the logical controller is also connected with the DSP extended bus interface.
 10. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 3, wherein said high speed digital signal processor comprises a digital signal processing chip, a dual port RAM, a static RAM, a logical controller, a host computer bus interface, and a DSP extended bus interface wherein said high speed digital signal processor chip is connected to one input terminal of the dual port RAM, the other input terminal of the dual port RAM is connected with the host computer bus interface, the digital signal processor chip is further connected with the static RAM and the DSP extended bus interface, the logical controller is connected with the digital signal processor chip, the static RAM, dual port RAM, and the host computer bus interface.
 11. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 3, wherein said I/O controller comprises an OC gate digital output port, an 8-bit digital input port, a timer, a logical controller, and a host computer bus interface, wherein said logical controller is connected with the host computer bus interface, the timer, the OC gate digital output port, the 8-bit digital input port, and the D/A converter.
 12. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 1 further comprising an overwater computer connected with host computer over an ethernet link.
 13. The high resolution bathymetric sidescan sonar system for measuring micro-geomorphy of the sea bottom according to claim 1, wherein said underwater vehicle is an AUV, ROV, towed system, or boat.
 14. A method for measuring micro-geomorphy of the sea bottom by using the high resolution bathymetric sidescan sonar system of claim 1, comprising (1) Selecting an underwater vehicle which is an AUV, a tethered ROV, a towed system, or a boat; (2) Drafting a preliminary overall specifications, combining a theoretical formula of a standard deviation of phase of a space-time correlation function of the sonar system with a sonar equation to perform a design, selecting main specifications, including an operation frequency, an action range, and a pulse width of the sonar system, and a length of the sonar array; (3) Based on a theoretical expression of a phase additional factor in the space-time correlation function of the sonar array, selecting a beam width of an element unit of the linear array of the sonar array and the space between the linear arrays, thus a good precision of measurement in measuring in a vicinity of a nadir of the sonar system is obtained; (4) Selecting the main specifications and repeating calculations in steps (2), (3) until the main specifications of the sonar system are fulfilled basically; (5) Making a decision on a number of the equal-spaced parallel linear arrays to be used, in which the number equals or greater than three, then performing an analogous calculation with an SBAD-MSADOAE method, determining preliminarily a resolution of the sonar system and an ability for overcoming a multipath effect; (6) Determining the main specifications of the sonar system, if the demands are not met, then the steps (2), (3), (4) and (5) are repeated, until the main specifications of the sonar system are determined, then manufacturing two prototypes of the sonar array; (7) Testing the two prototypes of the sonar array manufactured in step (6) in a pool; first, measuring echoes from a pool bottom, comparing the measured depth values of the pool with its true depth values, including the depth values of the pool in the vicinity of the nadir of the sonar system, the measured values should coincide well with the corresponding true values; second, measuring the outline of the pool including its wall corners, the measured values should coincide basically with the corresponding true values, then an out door tests may be performed; (8) Performing the tests on a lake or sea: testing the sonar array mounted on an underwater vehicle; performing the data processing after tests; first, comparing the depth values measured by the sonar in the vicinity of the nadir of the sonar system with the depth values measured by a high precision bathymeter, they should be coincidental well; second, operating the underwater vehicle in a case in which rather serious multipath effect exists, determining the ability of overcoming the multipath effect by the measured data, the correct depth values of the bottom of the water may be given on the finally obtained maps, without any multipath signal interference; (9) Merging the data measured by the sonar system with the data from an attitude sensor on the underwater vehicle and the positioning data to give a contour map; (10) Giving a grey scale map of an acoustic back scattering signal; (11) Making a map.
 15. A high resolution bathymetric sidescan system for measuring micro-geomorphy of the sea bottom comprising: an underwater electronic subsystem mounted on an underwater vehicle, said underwater electronic subsystem including: at least one transmitter; and at least one receiver; and a pair of sonar arrays mounted symmetrically on two sides of a lower part of the underwater vehicle connected to the underwater electronic subsystem, each of said sonar arrays including: a transmitting linear array connected to said transmitter; said transmitting array transmitting an acoustic wave toward the sea bottom; and at least three parallel equally spaced receiving linear arrays, each array being made of a piezoelectric ceramic material, connected to said receiver, the space between adjacent parallel receiving linear arrays being equal to d, where λ>d≧λ/2, and λ is the wavelength of the acoustic wave, the operation frequency of the parallel receiving linear arrays ranging from 30 kHz to 1200 kHz.
 16. The high resolution bathymetric sidescan sonar system according to claim 15, wherein the space between the adjacent parallel receiving linear arrays d is λ/2.
 17. The high resolution bathymetric sidescan sonar system according to claim 15, wherein said underwater electronic subsystem is provided with two transmitters and two receivers, the linear transmitting array of each of said pair of sonar arrays being connected electrically to one of said transmitters, and the receiving linear array of each of said pair of sonar arrays being connected electrically to one of said receivers, said underwater electronic subsystem further comprising: a multi-channel A/D converter having an input connected electrically to said receivers; a high speed digital signal processor connected electrically to said A/D converter; a host computer having a hard disk connected electrically to said high speed digital signal processor; and an I/O controller connected electrically with said host computer, said transmitters, and said receivers.
 18. The high resolution bathymetric sidescan sonar system according to claim 17, wherein said underwater electronic subsystem further comprises at least one of an attitude sensor and a temperature sensor, said attitude sensor and said temperature sensor being connected electrically to said host computer via said I/O controller, respectively. 